Volume up/down changes master AND wav

[carvell]

TV-Server Version:
MediaPortal Version: 0.2.3.0
MediaPortal Skin: default
Windows Version: XP SP2
CPU Type: AMD X2 5600+
HDD:
Memory: 2GB
Motherboard: ECS KA3 MVP
Motherboard Chipset: AMD 580X CrossFire
Motherboard Bios:
Video Card:
Video Card Driver:
Sound Card: Realtek Hi Def
Sound Card AC3:
Sound Card Driver:
1. TV Card: Hauppauge HVR-1300
1. TV Card Type:
1. TV Card Driver:
2. TV Card:
2. TV Card Type:
2. TV Card Driver:
3. TV Card:
3. TV Card Type:
3. TV Card Driver:
4. TV Card:
4. TV Card Type:
4. TV Card Driver:
MPEG2 Video Codec:
MPEG2 Audio Codec:
Satelite/CableTV Provider:
HTPC Case:
Cooling:
Power Supply:
Remote:
TV:
TV - HTPC Connection:

When I adjust the volume using the standard media portal up/down controls, both the master volume and the wav volume are changed. I definitely have mediaportal set to control the wav volume in the configuration, but when watching the sliders, they both change. Oddly, they don't always change in unison. For example I might nudge the mediaportal volume up a bit, the wav changes as you'd expect, but the master might go shooting right up to the stop and stay there.

It's a bit annoying because obviously it's not meant to do that, and it means I have to bring the master volume back down when I exit mediaportal.

Any ideas?